Recently, along with the advancement of communication in electromagnetic waves in the frequency region of microwaves, for example, in automobile telephones, in portable telephones, or in satellite braodcasts, apparatuses are required to be smaller. In order to attain this goal, each component comprising the apparatus must be miniaturized. In these apparatuses, a dielectric is inserted in a filter element or in an oscillation element in the form of a dielectric resonator. When using the same resonant mode, the size of the dielectric resonator is inversely proportional to the square root of the dielectric constant (.epsilon..sub.r) attributed to the dielectric material. Therefore, a material having a high dielectric constant is needed to manufacture a compact-sized dielectric resonator. In addition, in order to put a dielectric resonator into practice, the dielectric resonator must have low loss in the microwave region. In other words, the dielectric resonator must have a high Q value and a low temperature coefficient (.tau..sub.f) of a resonant frequency.
As a microwave dielectric used for a conventional dielectric resonator, a number of perovskite type ceramic compounds are disclosed, for example, in Published Examined Japanese Patent Application No. (Tokko Sho) 59-48484. These ceramic compounds contain Ba in A-site such as Ba(Zn.sub.1/3 Ta.sub.2/3)O.sub.3 type. These dielectrics have high Q values.
However, the above-mentioned dielectric ceramic compounds have the problem that the dielectric constants are as low as about 30 which is hardly practical for producing compact-sized dielectric resonators. Therefore, in order to reduce the size of the dielectric resonator, a dielectric having a higher dielectric constant, a high Q value, and a small temperature coefficient of resonant frequency has been in great demand.